perf/x86/amd/ibs: Don't include randomized bits in get_ibs_op_count()

get_ibs_op_count() adds hardware's current count (IbsOpCurCnt) bits
to its count regardless of hardware's valid status.

According to the PPR for AMD Family 17h Model 31h B0 55803 Rev 0.54,
if the counter rolls over, valid status is set, and the lower 7 bits
of IbsOpCurCnt are randomized by hardware.

Don't include those bits in the driver's event count.

Fixes: 8b1e13638d46 ("perf/x86-ibs: Fix usage of IBS op current count")
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 26c36357c4c9c6b809abb04d07e43aba80675bf3..863174ac0de377322969041f48b972c995f2d4f5 100644 (file)
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -334,11 +334,15 @@ static u64 get_ibs_op_count(u64 config)
 {
        u64 count = 0;
 
+       /*
+        * If the internal 27-bit counter rolled over, the count is MaxCnt
+        * and the lower 7 bits of CurCnt are randomized.
+        * Otherwise CurCnt has the full 27-bit current counter value.
+        */
        if (config & IBS_OP_VAL)
-               count += (config & IBS_OP_MAX_CNT) << 4; /* cnt rolled over */
-
-       if (ibs_caps & IBS_CAPS_RDWROPCNT)
-               count += (config & IBS_OP_CUR_CNT) >> 32;
+               count = (config & IBS_OP_MAX_CNT) << 4;
+       else if (ibs_caps & IBS_CAPS_RDWROPCNT)
+               count = (config & IBS_OP_CUR_CNT) >> 32;
 
        return count;
 }